It is well known to provide full complement anti-friction bearings. While such bearings have many advantages, they also have certain wear disadvantages. It is well known that the average load on a bearing is a radial load so that a bearing is considered to have a loaded zone between the races thereof in the area of load application and an unloaded zone diametrically remote from the loaded zone. The loaded and unloaded conditions of the bearing result in differential movement of the rolling elements relative to the races and produces undesirable wear characteristics.
First of all, in an anti-friction bearing utilizing solid rolling elements, the rolling elements must have a diameter slightly less than the radial spacing between the two raceways. As a result, when the rolling elements pass into the unloaded zone, they have little or no tendency to travel circumferentially relative to the relatively fixed one of the two raceways in that they are not in driven contact with the relatively rotating raceway. Accordingly, the rolling elements are pushed through the unloaded zone by the rolling elements disposed within the loaded zone. The net result is that the rolling elements are free to slide and do slide between the raceways in the unloaded zone and so cause wearing of flats thereon.
The fact that the rolling elements are not driven in the unloaded zone results in a speed up of the circumferential movement of the rolling elements as they approach the loading zone and pass therethrough with the maximum circumferential movement of the rolling elements. As the rolling elements begin to move out of the loading zone, they begin to progressively slow down with the result that the rolling elements are jammed together in the loaded zone and come into pressure contact with one another with the contacting surfaces rotating in opposite directions and wearing against one another.
It is also known that with full complement roller bearings, there is a tendency for the rollers to become skewed, that is non-parallel to the axis of the bearing, with the result that there is a tendency for the rollers to become wedged.
It is also to be understood that the sliding and rubbing of the rolling elements is detrimental to bearing life in that the increase in bearing friction results in a rise in temperature.
In the past, it has been recognized that with respect to anti-friction bearings wherein the rolling elements are mounted within a cage so that all of the rolling elements travel circumferentially in unison, the cage and the rolling elements are driven by those few rolling elements disposed in the loaded zone. While the provision of the cage has prevented rubbing contact between adjacent rolling elements, a new problem occurs. The driving force required to move the cage and roller complement circumferentially resists the rolling of the rolling elements through the loaded zone with the result that undue slip between the rolling elements and the driving raceway occurs. This is particularly true during the start up of the rotation of the bearing particularly when high acceleration exists.
This deficiency in caged roller bearings has been recognized in the past, and progressive efforts have been made to overcome the slippage between the rolling elements and the driving raceway. These include first forming a limited number of the rolling elements as cage driving members. For example, three of the rolling elements would be of a hollow construction with very little load sustaining ability, but of a diameter to be in constant pressure contact with the raceways at all times. This arrangement has a deficiency in that the load capability of the bearing was materially reduced. In a further development which is found in U.S. Pat. No. 3,410,618 to Tedric A. Harris, et al., granted Nov. 12, 1968, all of the rollers were made hollow and preloaded. Such an arrangement greatly improved the resistance to skidding.
However, none of these prior developments in any way suggested how one could overcome the deficiencies of full complement bearings.